In the case of a color image, the relative grayscale brightness of a pixel color is used. ?Normalize? means to stretch the contrast so that the
dimmest color is stretched to black and the brightest color is stretched to white, with all colors in between stretched out linearly. ?Histogram?
means to stretch the contrast based on a histogram of how many colors are at each brightness level on input, with the goal of producing equal
number of pixels in the image at each brightness level on output. This has the effect of revealing many subtle ground features. A ?GammaValue?
tells how much to brighten (value greater than 1.0) or dim (value less than 1.0) an image. The default GammaValue is 1.0 (no change). If none of
Normalize, Histogram, or GammaValue are selected in a ContrastEnhancement, then no enhancement is performed.